Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 krnk 221737 

Area forecast discussion
National Weather Service Blacksburg Virginia
1237 PM EST Wed Feb 22 2017

low pressure over the northern plains this morning will east
across the Great Lakes into New England through Thursday while
a low over the Gulf of Mexico will move across Florida. A strong
low forming in the Central Plains tonight and Thursday will
move northeast through the end of the week, pushing a warm front
into the Ohio Valley by Friday and an intense cold front across
the eastern United States on Saturday. High pressure will
follow the cold front for Sunday and Monday.


Near term /through tonight/...
as of 1005 am EST Wednesday...

Band of rain lined up from the Tennessee Valley into Virginia
this morning sets up well with the latest rap13 and hrrr. As
such adjusted pops a little higher in the southwest Virginia
area, northeastward toward Lynchburg, Virginia. As we head into the
afternoon, models showing less convergence in the Piedmont so
expect less coverage of rain, while the mountains, especially
south of I-81 into the NC mountains stay more in the rain,
eventually becoming less numerous after 3pm.

Temperatures running about 2-5 degrees cooler than previous
forecast. Not expecting any sunshine today, and think temps will
be cooler, so adjusted down the highs about 1-3 degrees. Still
for late February will be running about 5 to 10 degrees above

Previous discussion from early morning...

Area radars showed a band of rain from northern Virginia into
south central Kentucky early this morning. This band will move
slowly southeast today with the southern edge reaching the
Virginia/North Carolina border by 21z/4pm. Some isentropic lift
and a weak short wave will also generate light rain from the
southern Appalachians into the foothills of Virginia. Have
increased the probability of precipitation across the region
today. Also expecting fog along the Blue Ridge and into the
eastern foothills tonight and cloud bases lower.

At the surface a low over the northern Gulf of Mexico will track
across the Gulf then southern Florida today and tonight. This
will keep the best inflow of moisture off the Atlantic from
North Carolina to Georgia. Models still showed light southeast
wind from the surface through roughly 900mb but as a weak high
forms over the mid Atlantic region tonight wind speeds stay
light. But enough easterly component to the surface and low
level winds plus light precipitation to develop a shallow
in-situ wedge today. Have trimmed maximum temperatures up to 5
degrees today, staying below guidance at some locations, since
little to no sunshine expected.

Coverage of precipitation will diminish tonight but clouds and
fog will remain. Stayed close to cooler guidance for overnight


Short term /Thursday through Friday night/...
as of 350 am EST Wednesday...

High pressure off the North Carolina coast will continue to move
east into the Atlantic Ocean through Friday night. The general
prevailing flow across much of the region will be south to southwest
on the west side of this high.

An upper level disturbance will move northeast out of the Ohio Valley
and reach New England by Thursday night. Low level moisture will
advect into our area and result in plenty of clouds and patchy light
rain in areas primarily along the crest of the Blue Ridge. A warm
front will lift north across the region Thursday into Thursday
night. This will create scattered showers Thursday afternoon into
Thursday night. There is enough surface based instability as seen in
forecasted lifted index to support some isolated thunderstorms
across parts of southeast West Virginia, south into the northern
mountains of North Carolina. High temperatures on Thursday will
range from the upper 50s N the mountains to the lower 70s in the

Expect some patchy precipitation associated with the front Thursday
evening into Thursday night. Then, by early Friday morning, we
expect only some limited light rain near the crest of the Blue Ridge
as southerly flow yield some light upslope precipitation in this
area. Low temperature Thursday night will vary from the mid 40s in
the mountains to the lower 50s in the Piedmont.

Despite considerable clouds on Friday, it will be mild with readings
from the mid 60s in the mountains to the mid 70s in the Piedmont.
Elected to keep isolated showers along the Blue Ridge
mountains Friday.

For Friday night, a strong cold front will approach the area from
the west. Timing of front looked a little slower on this morning 00z
run vs the 12z run. Very strong southerly winds are progged to
increase in advance of this cold front. The potential for showers
will be on the increase through the night, especially across western
sections of the region. There appears to be enough instability for
isolated to scattered thunderstorms in the west. The day 3
convective outlook has highlighted a thunderstorm potential into
western portions of forecast area. Low temperatures Friday night
will range from the mid 40s in the mountains to the mid 50s in the


Long term /Saturday through Tuesday/...
as of 350 am EST Wednesday...

A strong cold front will cross the area on Saturday. Anticipate a
distinct line or area of showers to cross the region during the
course of the day, with coverage greatest across the northern third
of the region. Surface based instability may be great enough in the
afternoon for some isolated thunderstorms generally along and east
of a line from Danbury, NC to Bedford, Virginia.

Colder air will move into the area Saturday night. Gusty northwest
flow behind the cold front will help maintain isolated showers
across parts of southeast West Virginia that will transition to
isolated snow showers by late Saturday night. For Sunday, our
pattern transition to zonal flow aloft with surface high pressure
providing dry weather to the region.

The GFS is more robust with upslope for Saturday night into Sunday,
while European model (ecmwf) is drier with high pressure building in. Will hold on to
continuity with snow showers Saturday night, followed by high
pressure on Sunday.

Sunday night into Monday, a weak disturbance within this flow is
expected to bring isolated to scattered showers to the far western
parts of the area.

Monday night into Tuesday, southwest flow increases across the area
in advance of a developing upper level trough. Look for a warm front
to develop over the region and move northward. Anticipate cloud
cover and patchy light rain to develop across the region, and be
concentrated the greatest across the northern sections of the area,
nearest the warm front. Wednesday looked unsettled with scattered
showers continuing into Wednesday night.

Temperatures will still be some ten to twenty degrees above normal
on Saturday, but trend to near normal by Sunday behind the cold
front. Temperatures will slowly moderate Monday into Wednesday to
reading about ten degrees above normal.


Aviation /18z Wednesday through Monday/...
as of 1225 PM EST Wednesday...

Been dealing with variably changing aviation categories, with
in-situ wedge in place along with patchy rain/drizzle and fog.
At this forecast, the confidence stays below medium on the ever
changing cigs. Am confident enough over the eastern taf sites
including bcb/roa to bring cigs to MVFR to low end VFR at times
through this evening, with vsbys staying mainly 3sm or higher
with rain. Further west will see MVFR for most of the afternoon,
though some breaks in the low clouds occurs enough to have VFR
at times.

As we head through the overnight, model forecast soundings
suggest fog and/or low cigs. Will hit the fog harder in the east
with IFR occurring after 06z, with MVFR cigs. Across the
mountains will go more IFR cigs and vsbys.

Even LIFR fog/stratus may occur late in the bcb-blf-lwb area.

The shallow stable layer erodes as we head past 12-14z, such
that cigs/vsbys should improve, especially east of the
mountains. Some slower improvement at lwb so keeping them MVFR
between 15-18z Thu.

Extended aviation discussion...

Thursday afternoon should see mainly VFR except possible MVFR at
blf/lwb as showers approach.

Thursday night-Friday, we will be well into the warm sector
with VFR conditions and much above normal temperatures. Surface
wind gusts of 20 to 30 kts possible across the higher terrain.

Band of showers and isolated thunderstorms with MVFR conditions arrive
late Friday night into early Saturday along and ahead of a
strong cold front. Drier weather and increasing northwest winds
follow behind the front on Saturday afternoon through Sunday.

Approach of another front Monday will provide increasing clouds
and possibly showers and MVFR cigs to blf/lwb late in the day.


Rnk watches/warnings/advisories...


Synopsis...air mass

National Weather Service Glossary of Abbreviations